I developed a very large bruise after exercising, for apparantly no reason. Thought it was just muscle tenderness, but the black bruise on my buttocks, with a knot under it, proves otherwise. Can muscle strain cause severe bruising? Any suggestion would be appreciated.

A muscle strain is actually a tear of the fibers within the muscle belly or tendon. When you tear the muscle fibers, there is some bleeding. So, it is very possible to have a bruise after a strain.

The insertion of the hamstring muscles is located in the lower buttocks, just around the gluteal crease.

If you are taking blood thinners (coumadin) or are on NSAID's, it is much easier to have bruising after small injuries.

You can use some ice, in the early stages, to decrease the amount of bleeding. Once the bruising has been established, you can use heat to get the body to resorb to blood. Gentle stretching is also recommended, to help reduced the chances of developing scar tissues within the muscle belly.